A. Field of the Invention
This invention relates to television tuners, and more particularly, to UHF television tuners utilizing voltage variable capacitors to provide fine tuning and automatic frequency control.
B. Description of the Prior Art
UHF television tuners employing voltage variable capacitors for tuning and automatic frequency control are known. One such UHF tuner employs one or more voltage variable capacitors and a plurality of selectable potentiometers for applying a tuning voltage to the voltage variable capacitors. Each potentiometer is adjusted to tune the tuner to a preselected UHF television station, and station selection is achieved by selectively connecting the voltage variable capacitors within the tuner to the potentiometer corresponding to the desired channel. Automatic frequency control is obtained by coupling the automatic frequency control voltage to one of the voltage variable capacitors.
Other prior art UHF television tuners employ a voltage variable capacitor for automatic frequency control, but most utilize a mechanically actuated tuning element to achieve fine tuning, since the fine tuning range provided by voltage variable capacitors tends to be limited.
While these approaches make it possible to provide fine tuning and automatic frequency control for UHF television tuners, the systems using voltage variable capacitors for station selection tend to be inaccurate and prone to drift. Furthermore, a version capable of receiving all seventy UHF channels without readjustment of the tuning potentiometers would be quite complex and costly because of the large number of potentiometers required.
The UHF tuners using mechanically operated components for station selection have better accuracy and permit a seventy channel tuner to be built. One such tuner is described in U.S. Pat. No. 3,842,683. The mechanically tuned tuners utilizing a voltage variable capacitor for automatic frequency control, but retaining a mechanical fine tuning system usually employ a clutch, such as the system described in U.S. Pat. No. 3,774,459. Unfortunately, the clutch tends to slip when the detented selector shaft is turned, and results in a gradual detuning of the tuner. This phenomenon is commonly known as "creep".